SSH into the terminal and run command

sudo apt update

After the update completes downloading the package, run command

sudo apt upgrade

If you get an error:

E: dpkg was interrupted, you must manually run 'sudo dpkg --configure -a' to correct the problem

run the command as instructed

sudo dpkg --configure -a

then rerun the upgrade command

sudo apt upgrade

When it finishes upgrading, sync the version with command

sync

Then reboot GCP with command

sudo reboot

It will take some time for the instance to reboot. Mine took 5 minutes - when it comes back online do an uptime check to confirm that it rebooted.

uptime